Systems and methods for providing presence tracking in a distributed computing system

ABSTRACT

Providing presence tracking of nodes of a logical network in a distributed computing system. Each node in a logical network tracks the presence of all other nodes on the network. This presence information is used by the protocol to optimize bandwidth utilization of the shared physical media, by not attempting to communicate with a device that does not appear to be or is unlikely to be present. In one embodiment, the presence tracking is applied to a power line carrier (PLC) physical media because of PLC&#39;s low-bandwidth characteristics, low baud rate characteristics and the widespread usage of plugged-in devices, the presence of which on the network is generally more transient by nature.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/251,370, filed Sep. 19, 2002 (MSFT-1346/186575.01).

COPYRIGHT NOTICE AND PERMISSION

A portion of the disclosure of this patent document may contain materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent files or records, but otherwise reserves all copyrightrights whatsoever. The following notice shall apply to this document:Copyright ©1999-2002, Microsoft Corp.

FIELD OF THE INVENTION

The present invention is directed to systems and methods for providingpresence tracking of nodes of a logical network in a distributedcomputing system. More particularly, the present invention is directedto systems and methods for automatically tuning a logical network with“keep alive” optimization(s).

BACKGROUND OF THE INVENTION

Distributed computing is a field of study that has received increasedattention and study in recent years, as network interconnectivity, fromwired to wireless, of computing devices and objects continues to matureand computing devices and objects of all kinds continue to proliferate.To this end, a variety of protocols can be used to enable computingdevices and objects of all sorts to communicate with one another in amanner that is independent of the particularities of the source andtarget computing devices.

Examples of such protocols that have been developed include SimpleControl Protocol (SCP), x10, and CEBus®. SCP, for instance, is alightweight device-control protocol that allows manufacturers to createsmall, intelligent devices that can communicate with each other in asecure and robust manner over low-speed communication networks such ashousehold power lines. With SCP, devices with limited computing powerand memory resources—such as light switches, alarm clocks, andappliances—can be part of a peer-to-peer network of other SCP devices.Devices in an SCP network can also participate in more sophisticatedUniversal Plug and Play (UPnP) networks through a software componentcalled a UPnP to SCP bridge.

The following examples describe some typical scenarios that SCP andother protocols can make possible. Automated lights and light switchescan be enabled using SCP such that light switches and fixtures can becontrolled from a PC. A homeowner can change “which switches controlwhich lights” without needing to call an electrician to rewire thephysical circuits. Interactions among small appliances can also beenabled using SCP. For instance, an alarm clock can automatically starta coffee maker. Interactions among SCP and UPnP devices can also beenabled using SCP. For instance, a homeowner can place a tape in aUPnP-capable VCR and press “Play.” The VCR then sends a UPnP event to arules engine, which places the room into a home theater mode. The rulesengine then turns the UPnP TV on and connects it to the VCR audio andvideo outputs. Then, through an SCP to UPnP bridge, the engine tells theSCP room lights to dim and closes the SCP blinds.

One can thus readily see that SCP, and other protocols like SCP, arepowerful vehicles for communication across a variety of computingdevices. One can also appreciate that a variety of scenarios arepossible with SCP, when one considers the possibility of any computingdevice or object being able to communicate simply and easily with anyother computing device or object.

However, the above-described scenarios presume ideal, or near ideal,network conditions, and in contrast, often the actual physical mediumutilized for communications in a logical network is not ideal. Forinstance, in the case of power line communications, data is not alwaysguaranteed to arrive at its destination, or when it does, there may besome interference along the way that distorts the data or renders itunrecognizable. Similarly, on the reception side of data communications,interference can also be of impact. Moreover, various nodes may becomedisconnected from the network at widely variant rates, and thus, optimalpresence assertion refresh or timeout rates of a first node may bewidely different than optimal presence assertion refresh or timeoutrates of a second node on the same logical network. For instance,plug-in devices such as a table lamp may have different network behaviorcharacteristics from built-in devices, such as a furnace.

Accordingly, it would be desirable to minimize the number of failedmessaging communications by keeping a current list of nodes in thelogical network that are present and capable of receivingcommunications. It would be desirable, for instance, to skip messagingcommunications for nodes that are absent, and to prioritize messagesbased upon recency of presence and other assumption(s) or rule(s), whichmake messages more or less likely to arrive in a robust fashion. Inconnection with such logical network(s), therefore, it would bedesirable to provide presence tracking across logical network(s) fordynamic tuning of the logical network(s) according to messagingconditions, and rates of nodes appearing in or vanishing from thenetwork. It would be further desirable to provide an improvedoptimization of presence tracking variables across the logical networkfor lower bandwidth conditions.

SUMMARY OF THE INVENTION

In view of the foregoing, the present invention is directed to systemsand methods for providing presence tracking of nodes of a logicalnetwork in a distributed computing system. Each node in a logicalnetwork tracks the presence of all other nodes on the network. Thispresence information is used by the protocol to optimize bandwidthutilization of the shared physical media, by not attempting tocommunicate with a device that does not appear to be or is unlikely tobe present. In one embodiment, the presence tracking is applied to apower line carrier (PLC) physical media because of PLC's low-bandwidthcharacteristics, low baud rate characteristics and the widespread usageof plugged-in devices, the presence of which on the network is generallymore transient by nature. Each node on the network asserts its presenceby sending a periodic qualifying message and tracks the presence ofother nodes by periodically sampling whether a keep-alive has beenreceived.

In another embodiment, the invention tunes presence tracking on alogical network by splitting the logical network's node identification(node ID) address space in two parts, each part being assigned differentvalues for sending and sampling keep-alives. A first group of node IDsare assigned to “fast presence” devices, while a second group of nodeIDs part are assigned to “slow presence” devices. This process can bemanaged by an Address Space Arbitrator by using a hint value provided ineach device's description information.

Other features and embodiments of the present invention are describedbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The systems and methods for providing presence tracking of nodes of alogical network in a distributed computing system in accordance with thepresent invention are further described with reference to theaccompanying drawings in which:

FIG. 1 is a block diagram of one example of a protocol stack inconnection with which the invention may be implemented;

FIG. 2 is a block diagram illustrating exemplary aspects of securecommunications of a logical network in accordance with the invention;

FIG. 3A is a block diagram representing an exemplary network environmenthaving a variety of computing devices in which the present invention maybe implemented;

FIG. 3B is a block diagram representing an exemplary non-limitingcomputing device in which the present invention may be implemented;

FIG. 4A is a block diagram of a node presence tracking state flowdiagram;

FIG. 4B is an illustration of potential interplay between refresh andtimeout periodicities in accordance with the invention;

FIG. 5 is a block diagram of a node presence tracking data structure inaccordance with the invention; and

FIG. 6 is a flow diagram of exemplary use of presence trackingapplication variables and the two tiered assignment of nodes inaccordance with exemplary embodiments of the invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Overview

As described above, there is a need for improved presence tracking ofnodes in a logical network, particularly in connection with a low datarate or baud rate, less than ideal physical network underlying thelogical network, wherein low data rates, and transient presence hamperpresence tracking. A naive approach would be to frequently refresh thepresence of all nodes at the same rate; however, practically speaking,the assertion criteria for different kinds of nodes on the logicalnetwork should be flexible. The invention thus provides a simple, yetrobust, optimization of “keep alives” in connection with such a lowbandwidth, less than ideal physical network that enables dynamic tuningof logical network(s) according to messaging conditions, and rates ofnodes coming and going in the network.

In accordance with the invention, each node in a logical network, suchas Simple Control Protocol (SCP) network, tracks the presence of allother nodes on the network. This presence information is used by theprotocol to optimize bandwidth utilization of the shared physical media,by not attempting to communicate with device(s) which do not appear tobe present.

The invention recognizes that presence tracking can be especiallycritical on the power line carrier (PLC) physical media because of bothits low-bandwidth (and therefore baud rate) characteristics and of thewidespread usage of plugged-in devices, for which presence on thenetwork is generally more transient by nature. A logical network mayinclude built-in devices (a wall-mounted light control for example) andtransient devices (a plugged in table lamp for example) whichcommunicate with one another. Each node on an SCP network asserts itspresence by sending a periodic qualifying message or by sending trafficto other nodes; each node tracks the presence of every other node byperiodically sampling whether a keep-alive has been received from eachnode. A keep-alive for a node includes presence assertion by the nodeitself, or receipt of a qualifying message or packet from the node byanother portion of the logical network.

In one embodiment, the invention tunes presence tracking on a logicalnetwork by splitting the logical network's node identification (node ID)address space in two parts, each part being assigned different valuesfor sending and sampling keep-alives. The lower node IDs are assigned to“fast presence” devices, while upper node IDs part tracks “slowpresence” devices. This process can be actively managed by an AddressSpace Arbitrator (ASA) by using a hint value provided in each device'sdescription information.

Exemplary Logical Network—Overview of Simple Control Protocol (SCP)

As mentioned, embodiments of the invention apply to logical networks. Anoverview of SCP is provided herein. Various implementations of SCPsupport networks that use standard electrical wiring as the physicalmedium connecting the devices, e.g., the Power Line Carrier (PLC)implementation of SCP. Other SCP implementations for other physicalnetwork media such as radio frequency and infrared transmissions canalso be utilized.

FIG. 1 illustrates a block diagram overview of an exemplary SCP stack,and exemplary description of various aspects thereof follows. SCP is aprotocol that makes use of a physical medium 240, such as PLC. Aprotocol stack is a way to manage and organize nodes 200 in adistributed system via an API 210, or other object. A node 200 can beeither a software object or a hardware object, or a combination of both.One node, the address space arbitrator 200 asa, handles discovery,acquisition and maintenance of nodes on the logical network. There isone ASA 200 asa per logical network.

A protocol comprises an application protocol (AP) and a network controlprotocol. The application protocol side implements a session layer 215,a transport layer 220 and a network layer 225 which handle operations,transactions and messages, respectively. A data link layer 230 resideson top of the physical medium 240, and handles the message packets 235delivered and received by the network layer 225. A protocol encrypts anddecrypts communications for security purposes. Message communicationsmake use of a logical address that includes a net ID 300, a node ID 310and a network key 320, as illustrated in FIG. 2. These enable all nodesassociated in a logical network to share a secret, which allows for eachto communicate securely with other nodes on the logical network.

An SCP device is a component that uses the SCP to communicate with otherdevices connected to the same physical medium. SCP accommodates both“hard” and “soft” devices. A hard device is a piece of hardware such asa dimmer switch or a motion sensor. For hard devices, SCP is implementedas a set of integrated circuit (IC) chips that handle all of theprotocol-level communication tasks for a device. This chipset, whenadded to a device, forms a communication subsystem that handles of theprotocol-level communication tasks for the device.

A soft device is a software application that runs on a PC under the SCPdevice emulation environment. This environment emulates thecommunication subsystem provided by the SCP chipset and allows multiplesoft devices running on the same PC to share the same channel ofcommunications to the physical network.

At its simplest, an SCP network consists of two or more SCP devices andthe physical medium connecting the devices. A network can also includeother software components that run on a PC, such as the SCP to UPnPbridge, the Address-Space Arbitrator, and the Physical Network Manager.

The SCP to UPnP bridge is a special soft device that allows SCP devicesto interoperate with UPnP devices. The bridge extends the fullcapabilities of UPnP to small devices that are not capable ofimplementing TCP/IP and native UPnP stacks. For example, the bridgeallows the properties of an SCP device to be set by using messages sentacross a TCP/IP network. All SCP device property relationships areestablished at the UPnP level through the bridge and propagate down tothe SCP device level. The bridge also allows SCP devices to interoperatewith devices that use other control protocols. If a bridge existsbetween those devices and a UPnP network, SCP devices can use UPnP as acommon communication language.

The Address-Space Arbitrator (ASA) is another special soft device thatforms and manages a logical network of SCP devices. A logical network isa group of devices that are logically separate from other devicesconnected to the same physical network medium. SCP can support one ormore logical networks within the same physical network. For example, aphysical network can include a logical network for security devices,another for lighting devices, and yet another for audio-visualequipment. Logical networks are also used in environments such asapartment buildings where adjacent apartments share the same power line.Each apartment uses its own logical network so it does not interferewith the operation of the devices in a neighboring apartment.

The Physical Network Manager is a software component that runs on a PC.It manages the connection to the physical network, allowing multiplesoft devices running on the same PC to share the same connection.

An SCP device presents itself on the network as a root device withoptional nested sub-devices. Each device (or sub-device) supports one ormore services. A service consists of a group of related properties andactions. Properties describe the state of a service, and actions changeor access the state of a service. Taken together, the sub-devices,services, properties, and actions of a device are called its devicemodel. The SCP device model is analogous to a programming object, wherean object interface provides access to a set of properties and methodsthat operate on and describe the state of the object.

The SCP device model is based on the UPnP device model, e.g., the devicemodel for an SCP device is a UPnP device description that has beenaugmented with SCP data. As a device developer, a device model isdeveloped for the device, creating a binary version that the device usesat runtime.

SCP devices work by exposing their properties and actions to otherdevices, and by using operations to access the properties and actions ofother devices on the network. The operation is the fundamental unit ofcommunication among devices. A device uses operations to set andretrieve property values on other devices, to invoke actions on otherdevices, and to notify other devices when the value of a propertychanges.

Devices use operations to accomplish many tasks, and one of the primarytasks involves implementing subscriptions. A subscription is arelationship that one device, called the subscriber, sets up betweenitself and a property on another device, called the publisher. After asubscription is established, the publisher sends notification messagesto the subscriber whenever the value of the property changes.

Devices use subscriptions as the basis for setting up property routes. Aproperty route is a one-way connection between two properties: a sourceproperty on a publisher device and a destination property on asubscriber device. When the value of the source property changes onpublisher device, the subscriber device updates its destination propertywith the new value.

To illustrate how subscriptions and property routes work, consider adevice that exposes a simple timer service consisting of threeproperties: Increment, which specifies the timer countdown increment inmilliseconds; Value, which specifies the current countdown time; andTrigger, which changes from False to True when Value goes to zero. Theservice also has three actions: Start, Stop and SetValue. For example,if it is desired that the Timer turn on some lights when the Timer'sValue property goes to zero, a third-party (for example, a configurationutility) can tell each light to subscribe to the Timer's Triggerproperty and create a route between that property and the light'sIntensity property. Then, when Trigger property becomes True, eachlight's Intensity property also changes to True, and the lights come on.

One creates an SCP device by integrating the SCP communication subsysteminto the device. For a hard device, this involves incorporating the SCPchipset into the circuitry of the device. For a soft device, it involvesimplementing code in a Windows application that takes advantage of theSCP emulation environment.

The application subsystem connects to the SCP communication subsystemthrough a serial peripheral interface (SPI) connection. One of the maintasks (besides creating the device model) is to implement a softwareinterface to the SPI connection that allows the device application,running on the application processor, to communication with thecommunication subsystem. Code is also implemented that allows the deviceapplication to control the communication subsystem, using it tocommunicate with other devices on the network.

To summarize, creating an SCP device involves accomplishing thefollowing tasks. (1) Creating the device model that defines theservices, properties, and actions provided by the device, (2)Implementing code in your device application that supports the SPIconnection between the application subsystem and the SCP communicationsubsystem and (3) Implementing code in the application-processor thatinteracts with the communication subsystem to communicate with otherdevices in the network.

Commonly assigned copending U.S. patent application. Ser. No. 09/556,279(the '279 application), entitled “System for Networked Component Addressand Logical Network Formation and Maintenance” describes a system forforming and maintaining one or more networks of devices connected to ashared media is provided. Aspects of the '279 application includeprocesses for: (a) forming a logical network on the shared media; (b)discovering devices connected to the shared medium; (c) assigning (oracquiring) devices to a logical network; and (d) maintaining a logicalnetwork. Another aspect of the '279 application also defines a messageformat and protocol for communication over the shared media. Theprotocol uses a two-level address scheme (e.g., a logical network ID anda device ID) and defines several message types used to support the aboveprocesses and other useful features. Each device is expected to have aglobally unique device ID, called the Device Serial Number (DSN).

A logical network includes an address space arbiter (ASA) and,typically, one or more devices attached to the shared media. Anacquisition authority (AA), interacting with the ASA, is required tocomplete acquisition of a device by a logical network.

An ASA can form a logical network by selecting a possible logicalnetwork ID, when first attached to the physical media. The ASA thenbroadcasts a message addressed to the entire network to determinewhether the possible ID is already taken. If the possible ID is nottaken, the ASA adopts the ID as its logical network ID and can beginacquiring devices.

To join a logical network, a device attached to the shared mediabroadcasts an announce message addressed to the entire shared media.This is initiated at the request of an ASA attached to the shared media.ASAs receiving the announce message then determine whether the device isa “discovered” device. If the device is also not acquired, the AAdecides whether to authorize the ASA to acquire the discovered device.If authorized, the ASA then assigns an available device ID to thedevice. The device ID must be unique within the logical network, butdoes not necessarily have to be globally unique. The ASA helps maintainthe logical network by periodically sending a message to each device ofthe logical network and waiting for the appropriate response from thatdevice.

One advantage is that the system provides a simple way to segment ashared media into several logical networks. In addition, the systemprovides an easy-to-use mechanism for connecting devices to a networksuitable for the general public.

Exemplary Networked and Distributed Environments

One of ordinary skill in the art can appreciate that a computer or otherclient or server device can be deployed as part of a computer network,or in a distributed computing environment. In this regard, the presentinvention pertains to any computer system having any number of memory orstorage units, and any number of applications and processes occurringacross any number of storage units or volumes, which may be used inconnection with the keep alives optimization(s) of the invention. Thepresent invention may apply to an environment with server computers andclient computers deployed in a network environment or distributedcomputing environment, having remote or local storage. The presentinvention may also be applied to standalone computing devices, havingprogramming language functionality, interpretation and executioncapabilities for generating, receiving and transmitting information inconnection with remote or local services.

Distributed computing facilitates sharing of computer resources andservices by direct exchange between computing devices and systems. Theseresources and services include the exchange of information, cachestorage, and disk storage for files. Distributed computing takesadvantage of network connectivity, allowing clients to leverage theircollective power to benefit the entire enterprise. In this regard, avariety of devices may have applications, objects or resources that mayimplicate the keep alives optimization(s) of the invention.

FIG. 3A provides a schematic diagram of an e exemplary networked ordistributed computing environment. The distributed computing environmentcomprises computing objects 10 a, 10 b, etc. and computing objects ordevices 110 a, 110 b, 110 c, etc. These objects may comprise programs,methods, data stores, programmable logic, etc. The objects may compriseportions of the same or different devices such as PDAs, televisions, MP3players, televisions, personal computers, etc. Each object cancommunicate with another object by way of the communications network 14.This network may itself comprise other computing objects and computingdevices that provide services to the system of FIG. 3A. In accordancewith an aspect of the invention, each object 10 a, 10 b, etc. or 110 a,110 b, 110 c, etc. may contain an application that might make use of anAPI, or other object, software or hardware, to request use of the keepalives optimization(s) of the invention.

In a distributed computing architecture, computers, which may havetraditionally been used solely as clients, communicate directly amongthemselves and can act as both clients and servers, assuming whateverrole is most efficient for the network. This reduces the load on serversand allows all of the clients to access resources available on otherclients, thereby increasing the capability and efficiency of the entirenetwork. Services that use the keep alives optimization(s) in accordancewith the present invention may thus be distributed among clients andservers, acting in a way that is efficient for the entire network.

Distributed computing can help businesses deliver services andcapabilities more efficiently across diverse geographic boundaries.Moreover, distributed computing can move data closer to the point wheredata is consumed acting as a network caching mechanism. Distributedcomputing also allows computing networks to dynamically work togetherusing intelligent agents. Agents reside on peer computers andcommunicate various kinds of information back and forth. Agents may alsoinitiate tasks on behalf of other peer systems. For instance,intelligent agents can be used to prioritize tasks on a network, changetraffic flow, search for files locally or determine anomalous behaviorsuch as a virus and stop it before it affects the network. All sorts ofother services may be contemplated as well. Since data may in practicebe physically located in one or more locations, the ability todistribute services that make use of the keep alives optimization(s)described herein is of great utility in such a system.

It can also be appreciated that an object, such as 110 c, may be hostedon another computing device 10 a, 10 b, etc. or 110 a, 110 b, etc. Thus,although the physical environment depicted may show the connecteddevices as computers, such illustration is merely exemplary and thephysical environment may alternatively be depicted or describedcomprising various digital devices such as PDAs, televisions, MP3players, etc., software objects such as interfaces, COM objects and thelike.

There are a variety of systems, components, and network configurationsthat support distributed computing environments. For example, computingsystems may be connected together by wired or wireless systems, by localnetworks or widely distributed networks. Currently, many of the networksare coupled to the Internet, which provides the infrastructure forwidely distributed computing and encompasses many different networks.

In home networking environments, there are at least four disparatenetwork transport media that may each support a unique protocol, such asPower line, data (both wireless and wired), voice (e.g., telephone) andentertainment media. Most home control devices such as light switchesand appliances may use power line for connectivity. Data Services mayenter the home as broadband (e.g., either DSL or Cable modem) and areaccessible within the home using either wireless (e.g., HomeRF or802.11b) or wired (e.g., Home PNA, Cat 5, even power line) connectivity.Voice traffic may enter the home either as wired (e.g., Cat 3) orwireless (e.g., cell phones) and may be distributed within the homeusing Cat 3 wiring. Entertainment media, or other graphical data, mayenter the home either through satellite or cable and is typicallydistributed in the home using coaxial cable. IEEE 1394 and DVI are alsoemerging as digital interconnects for clusters of media devices. All ofthese network environments and others that may emerge as protocolstandards may be interconnected to form an intranet that may beconnected to the outside world by way of the Internet. In short, avariety of disparate sources exist for the storage and transmission ofdata, and consequently, moving forward, computing devices will requireways of sharing data, such as data accessed or utilized incident toprogram objects, which make use of keep alives optimization(s) inaccordance with the present invention.

The Internet commonly refers to the collection of networks and gatewaysthat utilize the TCP/IP suite of protocols, which are well-known in theart of computer networking. TCP/IP is an acronym for “Transport ControlProtocol/Interface Program.” The Internet can be described as a systemof geographically distributed remote computer networks interconnected bycomputers executing networking protocols that allow users to interactand share information over the networks. Because of such wide-spreadinformation sharing, remote networks such as the Internet have thus fargenerally evolved into an open system for which developers can designsoftware applications for performing specialized operations or services,essentially without restriction.

Thus, the network infrastructure enables a host of network topologiessuch as client/server, peer-to-peer, or hybrid architectures. The“client” is a member of a class or group that uses the services ofanother class or group to which it is not related. Thus, in computing, aclient is a process, i.e., roughly a set of instructions or tasks, thatrequests a service provided by another program. The client processutilizes the requested service without having to “know” any workingdetails about the other program or the service itself. In aclient/server architecture, particularly a networked system, a client isusually a computer that accesses shared network resources provided byanother computer, e.g., a server. In the example of FIG. 3A, computers110 a, 110 b, etc. can be thought of as clients and computer 10 a, 10 b,etc. can be thought of as the server where server 10 a, 10 b, etc.maintains the data that is then replicated in the client computers 110a, 110 b, etc.

A server is typically a remote computer system accessible over a remotenetwork such as the Internet. The client process may be active in afirst computer system, and the server process may be active in a secondcomputer system, communicating with one another over a communicationsmedium, thus providing distributed functionality and allowing multipleclients to take advantage of the information-gathering capabilities ofthe server.

Client and server communicate with one another utilizing thefunctionality provided by a protocol layer. For example,Hypertext-Transfer Protocol (HTTP) is a common protocol that is used inconjunction with the World Wide Web (WWW). Typically, a computer networkaddress such as a Universal Resource Locator (URL) or an InternetProtocol (IP) address is used to identify the server or client computersto each other. The network address can be referred to as a URL address.For example, communication can be provided over a communications medium.In particular, the client and server may be coupled to one another viaTCP/IP connections for high-capacity communication. SCP, x10 and CEBus®are other examples of protocols used for logical network(s).

Thus, FIG. 3A illustrates an exemplary networked or distributedenvironment, with a server in communication with client computers via anetwork/bus, in which the present invention may be employed. In moredetail, a number of servers 10 a, 10 b, etc., are interconnected via acommunications network/bus 14, which may be a LAN, WAN, intranet, theInternet, etc., with a number of client or remote computing devices 110a, 110 b, 110 c, 110 d, 110 e, etc., such as a portable computer,handheld computer, thin client, networked appliance, or other device,such as a VCR, TV, oven, light, heater and the like in accordance withthe present invention. It is thus contemplated that the presentinvention may apply to any computing device in connection with which itis desirable to implement logical network(s).

In a network environment in which the communications network/bus 14 isthe Internet, for example, the servers 10 a, 10 b, etc. can be Webservers with which the clients 110 a, 110 b, 110 c, 110 d, 110 e, etc.communicate via any of a number of known protocols such as HTTP. Servers10 a, 10 b, etc. may also serve as clients 110 a, 110 b, 110 c, 110 d,110 e, etc., as may be characteristic of a distributed computingenvironment. Communications may be wired or wireless, where appropriate.Client devices 110 a, 110 b, 110 c, 110 d, 110 e, etc. may or may notcommunicate via communications network/bus 14, and may have independentcommunications associated therewith. For example, in the case of a TV orVCR, there may or may not be a networked aspect to the control thereof.Each client computer 110 a, 110 b, 110 c, 110 d, 110 e, etc. and servercomputer 10 a, 10 b, etc. may be equipped with various applicationprogram modules or objects 135 and with connections or access to varioustypes of storage elements or objects, across which files may be storedor to which portion(s) of files may be downloaded or migrated. Anycomputer 10 a, 10 b, 110 a, 110 b, etc. may be responsible for themaintenance and updating of a database 20 or other storage element inaccordance with the present invention, such as a database or memory 20for storing application variable(s) or data processed according to theinvention. Thus, the present invention can be utilized in a computernetwork environment having client computers 110 a, 110 b, etc. that canaccess and interact with a computer network/bus 14 and server computers10 a, 10 b, etc. that may interact with client computers 110 a, 110 b,etc. and other like devices, and databases 20.

Exemplary Computing Device

FIG. 3B and the following discussion are intended to provide a briefgeneral description of a suitable computing environment in which theinvention may be implemented. It should be understood, however, thathandheld, portable and other computing devices and computing objects ofall kinds are contemplated for use in connection with the presentinvention. While a general purpose computer is described below, this isbut one example, and the present invention may be implemented with athin client having network/bus interoperability and interaction. Thus,the present invention may be implemented in an environment of networkedhosted services in which very little or minimal client resources areimplicated, e.g., a networked environment in which the client deviceserves merely as an interface to the network/bus, such as an objectplaced in an appliance. In essence, anywhere that data may be stored orfrom which data may be retrieved is a desirable, or suitable,environment for operation of the techniques utilizing keep alivesoptimization(s) of the invention.

Although not required, the invention can be implemented via an operatingsystem, for use by a developer of services for a device or object,and/or included within application software that operates in connectionwith keep alives optimization(s) of the invention. Software may bedescribed in the general context of computer-executable instructions,such as program modules, being executed by one or more computers, suchas client workstations, servers or other devices. Generally, programmodules include routines, programs, objects, components, data structuresand the like that perform particular tasks or implement particularabstract data types. Typically, the functionality of the program modulesmay be combined or distributed as desired in various embodiments.Moreover, those skilled in the art will appreciate that the inventionmay be practiced with other computer system configurations andprotocols. Other well known computing systems, environments, and/orconfigurations that may be suitable for use with the invention include,but are not limited to, personal computers (PCs), automated tellermachines, server computers, hand-held or laptop devices, multi-processorsystems, microprocessor-based systems, programmable consumerelectronics, network PCs, appliances, lights, environmental controlelements, minicomputers, mainframe computers and the like. The inventionmay also be practiced in distributed computing environments where tasksare performed by remote processing devices that are linked through acommunications network/bus or other data transmission medium. In adistributed computing environment, program modules may be located inboth local and remote computer storage media including memory storagedevices, and client nodes may in turn behave as server nodes.

FIG. 3B thus illustrates an example of a suitable computing systemenvironment 100 in which the invention may be implemented, although asmade clear above, the computing system environment 100 is only oneexample of a suitable computing environment and is not intended tosuggest any limitation as to the scope of use or functionality of theinvention. Neither should the computing environment 100 be interpretedas having any dependency or requirement relating to any one orcombination of components illustrated in the exemplary operatingenvironment 100.

With reference to FIG. 3B, an exemplary system for implementing theinvention includes a general purpose computing device in the form of acomputer 110. Components of computer 110 may include, but are notlimited to, a processing unit 120, a system memory 130, and a system bus121 that couples various system components including the system memoryto the processing unit 120. The system bus 121 may be any of severaltypes of bus structures including a memory bus or memory controller, aperipheral bus, and a local bus using any of a variety of busarchitectures. By way of example, and not limitation, such architecturesinclude Industry Standard Architecture (ISA) bus, Micro ChannelArchitecture (MCA) bus, Enhanced ISA (EISA) bus, Video ElectronicsStandards Association (VESA) local bus, and Peripheral ComponentInterconnect (PCI) bus (also known as Mezzanine bus).

Computer 110 typically includes a variety of computer readable media.Computer readable media can be any available media that can be accessedby computer 110 and includes both volatile and nonvolatile media,removable and non-removable media. By way of example, and notlimitation, computer readable media may comprise computer storage mediaand communication media. Computer storage media includes both volatileand nonvolatile, removable and non-removable media implemented in anymethod or technology for storage of information such as computerreadable instructions, data structures, program modules or other data.Computer storage media includes, but is not limited to, RAM, ROM,EEPROM, flash memory or other memory technology, CDROM, digitalversatile disks (DVD) or other optical disk storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,or any other medium which can be used to store the desired informationand which can accessed by computer 110. Communication media typicallyembodies computer readable instructions, data structures, programmodules or other data in a modulated data signal such as a carrier waveor other transport mechanism and includes any information deliverymedia. The term “modulated data signal” means a signal that has one ormore of its characteristics set or changed in such a manner as to encodeinformation in the signal. By way of example, and not limitation,communication media includes wired media such as a wired network ordirect-wired connection, and wireless media such as acoustic, RF,infrared and other wireless media. Combinations of any of the aboveshould also be included within the scope of computer readable media.

The system memory 130 includes computer storage media in the form ofvolatile and/or nonvolatile memory such as read only memory (ROM) 131and random access memory (RAM) 132. A basic input/output system 133(BIOS), containing the basic routines that help to transfer informationbetween elements within computer 110, such as during start-up, istypically stored in ROM 131. RAM 132 typically contains data and/orprogram modules that are immediately accessible to and/or presentlybeing operated on by processing unit 120. By way of example, and notlimitation, FIG. 3B illustrates operating system 134, applicationprograms 135, other program modules 136, and program data 137.

The computer 110 may also include other removable/non-removable,volatile/nonvolatile computer storage media. By way of example only,FIG. 3B illustrates a hard disk drive 141 that reads from or writes tonon-removable, nonvolatile magnetic media, a magnetic disk drive 151that reads from or writes to a removable, nonvolatile magnetic disk 152,and an optical disk drive 155 that reads from or writes to a removable,nonvolatile optical disk 156, such as a CD-ROM or other optical media.Other removable/non-removable, volatile/nonvolatile computer storagemedia that can be used in the exemplary operating environment include,but are not limited to, magnetic tape cassettes, flash memory cards,digital versatile disks, digital video tape, solid state RAM, solidstate ROM and the like. The hard disk drive 141 is typically connectedto the system bus 121 through a non-removable memory interface such asinterface 140, and magnetic disk drive 151 and optical disk drive 155are typically connected to the system bus 121 by a removable memoryinterface, such as interface 150.

The drives and their associated computer storage media discussed aboveand illustrated in FIG. 3B provide storage of computer readableinstructions, data structures, program modules and other data for thecomputer 110. In FIG. 3B, for example, hard disk drive 141 isillustrated as storing operating system 144, application programs 145,other program modules 146, and program data 147. Note that thesecomponents can either be the same as or different from operating system134, application programs 135, other program modules 136, and programdata 137. Operating system 144, application programs 145, other programmodules 146, and program data 147 are given different numbers here toillustrate that, at a minimum, they are different copies. A user mayenter commands and information into the computer 110 through inputdevices such as a keyboard 162 and pointing device 161, commonlyreferred to as a mouse, trackball or touch pad. Other input devices (notshown) may include a microphone, joystick, game pad, satellite dish,scanner, or the like. These and other input devices are often connectedto the processing unit 120 through a user input interface 160 that iscoupled to the system bus 121, but may be connected by other interfaceand bus structures, such as a parallel port, game port or a universalserial bus (USB). A graphics interface 182, such as Northbridge, mayalso be connected to the system bus 121. Northbridge is a chipset thatcommunicates with the CPU, or host processing unit 120, and assumesresponsibility for accelerated graphics port (AGP) communications. Oneor more graphics processing units (GPUs) 184 may communicate withgraphics interface 182. In this regard, GPUs 184 generally includeon-chip memory storage, such as register storage and GPUs 184communicate with a video memory 186, wherein the keep alivesoptimization(s) of the invention may have impact. GPUs 184, however, arebut one example of a coprocessor and thus a variety of coprocessingdevices may be included in computer 110, and may include a variety ofprocedural shaders, such as pixel and vertex shaders. A monitor 191 orother type of display device is also connected to the system bus 121 viaan interface, such as a video interface 190, which may in turncommunicate with video memory 186. In addition to monitor 191, computersmay also include other peripheral output devices such as speakers 197and printer 196, which may be connected through an output peripheralinterface 195.

The computer 110 may operate in a networked or distributed environmentusing logical connections to one or more remote computers, such as aremote computer 180. The remote computer 180 may be a personal computer,a server, a router, a network PC, a peer device or other common networknode, and typically includes many or all of the elements described aboverelative to the computer 110, although only a memory storage device 181has been illustrated in FIG. 3B. The logical connections depicted inFIG. 3B include a local area network (LAN) 171 and a wide area network(WAN) 173, but may also include other networks/buses. Such networkingenvironments are commonplace in homes, offices, enterprise-wide computernetworks, intranets and the Internet.

When used in a LAN networking environment, the computer 110 is connectedto the LAN 171 through a network interface or adapter 170. When used ina WAN networking environment, the computer 110 typically includes amodem 172 or other means for establishing communications over the WAN173, such as the Internet. The modem 172, which may be internal orexternal, may be connected to the system bus 121 via the user inputinterface 160, or other appropriate mechanism. In a networkedenvironment, program modules depicted relative to the computer 110, orportions thereof, may be stored in the remote memory storage device. Byway of example, and not limitation, FIG. 3B illustrates remoteapplication programs 185 as residing on memory device 181. It will beappreciated that the network connections shown are exemplary and othermeans of establishing a communications link between the computers may beused.

Exemplary Distributed Computing Frameworks or Architectures

Various distributed computing frameworks have been and are beingdeveloped in light of the convergence of personal computing and theInternet. Individuals and business users alike are provided with aseamlessly interoperable and Web-enabled interface for applications andcomputing devices, making computing activities increasingly Web browseror network-oriented.

For example, MICROSOFT®'s .NET platform includes servers, building-blockservices, such as Web-based data storage and downloadable devicesoftware. Generally speaking, the .NET platform provides (1) the abilityto make the entire range of computing devices work together and to haveuser information automatically updated and synchronized on all of them,(2) increased interactive capability for Web sites, enabled by greateruse of XML rather than HTML, (3) online services that feature customizedaccess and delivery of products and services to the user from a centralstarting point for the management of various applications, such ase-mail, for example, or software, such as Office .NET, (4) centralizeddata storage, which will increase efficiency and ease of access toinformation, as well as synchronization of information among users anddevices, (5) the ability to integrate various communications media, suchas e-mail, faxes, and telephones, (6) for developers, the ability tocreate reusable modules, thereby increasing productivity and reducingthe number of programming errors and (7) many other cross-platformintegration features as well.

Automatic Network Optimization Using Keep Alives Optimization(s)

In accordance with the invention, each node in a logical network tracksthe presence of all other nodes on the network. This presenceinformation is used by the protocol to optimize bandwidth utilization ofthe shared physical media, by not attempting to communicate with adevice which does not appear to be present.

With further reference to FIG. 1, the Network layer 225 in each nodetracks the presence of all other nodes in its logical network. The DataLink layer 230 supports this capability. The Data Link layer 230 passesall packets up to the Network layer 225, including unicast packetstargeting other devices. The Network layer 225 is also supported byspecial messages from Network Control Protocol (NCP) 250 that are usedto indicate when a node 200 comes online, goes offline in a gracefulway, and signals its continued presence, e.g., when it has not sent anyother packets for a certain amount of time. Node presence tracking mayrun in either robust or unsecured mode. In unsecured mode (address inthe clear), any packet sent qualifies to indicate its presumedoriginator is present on the logical network, while in robust mode, onlyauthentic and time stamped messages qualify.

In one embodiment, each node keeps track of the presence states of othernodes in the logical network, as per the exemplary non-limiting presencestate flow diagram of FIG. 4A. In FIG. 4A, at startup, each node trackedis placed in the “presumed present” state 400. Once qualifying trafficis received from that node anywhere on the logical network, or when thenode asserts its presence, i.e., signs on, the node is placed in the“present” state 410. If, however, a failed transaction implicating ortargeting the node fails, the node is considered to have entered the“absent” state 420. Similarly, if nothing, e.g., no keep alive message,is heard from the node for a predetermined amount of time, i.e., thenode times out, the node is considered to have entered the absent state420. Moreover, if the node signs off, the node is placed in the absentstate 420.

Once in the present state 410, if a failed transaction implicating ortargeting the node fails, the node is considered to have entered theabsent state 420. Similarly, if the node signs off, the node isconsidered to have entered the absent state 420. Another way for thenode to leave the present state is if a predetermined period of timepasses, i.e., if a timeout occurs, without hearing from the node. Insuch a case, the node leaves the present state 410 for the “was present”state 430. In such circumstances, the node is given special treatmentsince the node was in fact heard from at some point due to actualtraffic from the node, but the timeout condition has been reached. Sincetimeout may have occurred due to a temporary network aberration asopposed to the node's actual absence, the node is not placed in theabsent state 420, but rather is placed into the intermediate was presentstate 430.

Once in the was present state 430, as a result of a timeout from thepresent state 410, a node re-enters the present state 410 as a result ofthe receipt of keep-alive or sign on message from the node. If, however,an additional pre-determined period of time occurs without hearing fromthe node, then a sufficient period of time has passed such that the nodecan be considered to have entered the absent state 420. Moreover, if afailed transaction implicating or targeting the node fails while thenode is in the was present state 430, the node is then considered tohave entered the absent state 420. From the absent state 420, the nodecan only enter the present state 410 upon receipt of a keep alive orsign on message from the node. A node can also enter the absent state420 by sending a sign off message from any other state. How often a nodesends refresh traffic and how long the timeout conditions are can be setas network tuning parameters. Also, as will be appreciated from otherembodiments below, some devices merit different settings based upontheir characteristic behavior on the network. In one embodiment, thefour states, i.e., presumed present 400, present 410, was present 430and absent 420, are represented with 2 bits. Thus, for instance, in alogical network comprising 2048 nodes, only 512 bytes are required torepresent presence information. This is suited for an SCP/PLCimplementation on an embedded microcontroller with limited memoryresources, such as RAM, as noted above.

As illustrated in FIG. 4B, an exemplary non-limiting choice for atimeout period to refresh period ratio is 2.5, such that there is thepossibility of missing a refresh message on the network without removingthe node from the present state 410. Additionally, even if two or threerefresh messages are missed, the node is not placed in the absent state420 until 5 or more refresh messages are missed due to the existence ofthe intermediate was present state 430.

As mentioned above, the presence tracking model of the invention workswell with power line carrier (PLC) physical media because of both itslow-bandwidth (and therefore low baud rate) characteristics and of thewidespread usage of plugged-in devices, for which presence can be atransient quality. Thus, with respect to an exemplary implementation inan SCP network, each node on an SCP network asserts its presence bysending a qualifying message (keep-alive) at least every PresenceRefreshseconds and each node tracks the presence of every other node bysampling every PresenceTimeout seconds whether a keep-alive has beenreceived from each node. As noted above, an exemplary non-limitingheuristic choice is for PresenceTimeout to be set to greater than orequal to 2.0 times PresenceRefresh. This heuristic choice is intended inno way to limit the scope of the invention.

The invention thus enables a framework for tuning presence tracking on alogical network. In one embodiment, the invention additionally splitsthe logical network's node identification (node ID) address space in twoparts, with each part being assigned different values forPresenceRefresh and PresenceTimeout. In this regard, and as illustratedin the exemplary data structure of FIG. 5, presence information isstored for a given node, which are indexed by nodeID. Devices storedabove the SlowBaseID are considered fast devices, and devices storedbelow the SlowBaseID are considered slow. Alternatively, the lower nodeIDs can also be assigned to “fast presence” devices, while upper nodeIDs can track “slow presence” devices. In one embodiment, this processis actively managed by the SCP Address Space Arbitrator, which isdescribed in further detail in commonly assigned copending U.S. patentapplication. No. AA/BBB,CCC, filed MM/DD/YYYY (ASA, 186568.1),incorporated herein by reference, by using a hint value calledPresenceLease provided in each SCP device's description information.

The invention thus enables the optimization of network bandwidthutilized for presence tracking in what are real-world scenarios forprotocols using less than ideal physical media, such as SCP/PLC.

In an embodiment of the invention relating to SCP, SCP's network layerprotocol implements a presence tracker, which runs independently on eachnode. The behavior of the presence tracker is affected by fiveapplication variables, described in U.S. patent application. No.XX/YYY,ZZZ (the 'ZZZ application), filed Month Day, Year, entitled“Systems and Methods for Providing Automatic Network Optimization withApplication Variables,” incorporated herein by reference, identified asfollows:

-   -   1. eScpAPVars_Net_PresenceSlowBaseld, the node ID where the        logical split between fast coming and going devices and slow        coming and going devices occurs;    -   2. eScpAPVars_Net_PresenceFastRefresh, the PresenceRefresh value        to be used to track devices with a node ID less than the value        specified by eScpAPVars_Net_PresenceSlowBaseId    -   3. eScpAPVars_Net_PresenceFastTimeout, the PresenceTimeout value        to be used to track devices with a node ID less than the value        specified by eScpAPVars_Net_PresenceSlowBaseId    -   4. eScpAPVars_Net_PresenceSlowRefresh, the PresenceRefresh value        to be used to track devices with a node ID greater or equal than        the value specified by eScpAPVars_Net_PresenceSlowBaseId    -   5. eScpAPVars_Net_PresenceSlowTimeout, the PresenceTimeout value        to be used to track devices with a node ID greater or equal than        the value specified by eScpAPVars_Net_PresenceSlowBaseId

In one embodiment, the presence tracker polls the value of theseapplication variables at certain times, such as every time they areused, since they may be modified asynchronously by the ASA.

In a preferred non-limiting embodiment, the presence tracker performsthe following tasks in this order of priority:

-   -   1. A keep-alive message is sent if PresenceRefresh seconds have        gone by since the last keep alive was sent. The PresenceRefresh        is either eScpAPVars_Net_PresenceFastRefresh if the node ID is        less than eScpAPVars_Net_PresenceSlowBaseId or        eScpAPVars_Net_PresenceSlowRefresh if the node ID is greater        than or equal to eScpAPVars_Net_PresenceSlowBaseId.    -   2. Every eScpAPVars_Net_PresenceFastTimeout it scans the        presence table up to eScpAPVars_Net_PresenceSlowBaseId and        declares any node for which a keep alive has not been received        since the last sampling and in the presumed present or was        present state as absent and declares any node in the present        state as was present.    -   3. Every eScpAPVars_Net_PresenceSlowTimeout it scans the        presence table from eScpAPVars_Net_PresenceSlowBaseId and        declares any node for which a keep alive has not been received        since the last sampling and in the presumed present or was        present state as absent and declares any node in the present        state as was present.

FIG. 6 illustrates an exemplary non-limiting flow diagram that makes useof the concept(s) described above. At 600, a presence tracker of a nodeor device resets counters. At 605, counters are updated with an elapsedtime (initially zero) and processing to other tasks yields for theupdate. At 610, a determination is made whether the nodeID of a node isless than the SlowBasedID. If so, at 615, the refresh TimeOut value forthe node is set to the fast time out value. If not, at 625, the refreshtime out value is set to the slow time out value. At 630, adetermination is made whether a refresh counter is greater than therefresh TimeOut value. If so, a keep alive message is sent and therefresh counter is reset at 635, and the flow proceeds to 640. If not,the flow proceeds to 640, where a determination is made whether the fastpresence counter is greater than the presence fast timeout variable. Ifso, at 645, the presence table is scanned up to the SlowBaseID and everynode tracked node is declared as less present. In one embodiment, theterm “less present” is construed differently for different nodesdepending upon their presence states. For nodes that are in the waspresent or presumed present state, the presence table is scanned up tothe SlowBaseID and any node for which a keep alive has not been receivedsince the last sampling is declared as absent. For a node that are inthe present state, the presence table is scanned up to the SlowBaseIDand the node is declared as “was present.” having a less present statethan previously, i.e., for a node that is presumed present, the node isdeclared as absent and for a node that is “was present,” the node isdeclared as absent. For a node that is present, the presence table isscanned up to the SlowBaseID and the node is declared as “was present.”The fast presence counter is also reset and the flow proceeds to 650. Ifnot, the flow proceeds to 650, where a determination is made whether theslow presence counter is greater than the presence slow timeoutvariable. If so, at 645, the presence table is scanned up to theSlowBaseID and every node tracked node is declared as less present. Fornodes that are in the was present or presumed present state, thepresence table is scanned up to the SlowBaseID and any node for which akeep alive has not been received since the last sampling is declared asabsent. For a node that are in the present state, the presence table isscanned up to the SlowBaseID and the node is declared as “was present.”The slow presence counter is also reset and the flow proceeds to 605. Ifnot, the flow proceeds to 605.

As mentioned above, presence tracking may run in either robust orunsecured mode. In unsecured mode, any packet sent qualifies to indicateits presumed originator is present on the logical network, while inrobust mode, only authentic and time stamped messages qualify.

The address space is separated in two groups of devices: those that tendto time out quickly and those that tend to time out slowly,respectively. In one embodiment, the ASA controls the operating mode andthe quick vs. slow devices using application variables.

With respect to presence notifications, various embodiments can beimplemented. In one embodiment, the Network layer notifies the higherlayers of the following events for a given node: (A) the node justsigned on, (B) the node appeared on the logical network, (C) the nodevanished from the logical network (timing out), (D) the node presence isplaced into the absent state on that node and (E) the node signed off.

These rules help to prevent wasted communication effort and channelbandwidth, as well as stalled message transmission, until SCP detectsactivity on the part of the node again. The cycle of forcing the absentstate, and then re-appearance due to activity, causes a higher layerretry cycle.

An asymmetric (one way) communication fault between two nodes that lastslonger than the maximum time a node is allowed to be silent can cause acorresponding asymmetry in device presence and thus error controlprotocols used with the node presence mechanism of the invention canoptionally take this case into consideration.

It can be appreciated that even at power loss, it is desirable for anode to send an Network Control Protocol sign off message. However, thismay not always be possible due to network delays beyond the device'spower hold-up time, unacceptable cost of power hold-up components, orabrupt network disconnection (e.g., yanking the plug out of the wallsocket), etc.

In robust mode, SCP bases node presence or absence upon the followingmessages, in the event that the messages are authentic and time stampedwith a valid network time: Any application protocol (AP) message thatfits in a single packet, whether unicast, multicast or broadcast to thelogical network, including (A) an NCP_NetSignOn message, (B) anNCP_NetTimeAssert message, tunneled in an AP packet which is not checkedfor a valid time stamp, (C) an NCP_NetSignOff message and (D) anNCP_NetPresence message.

In unsecured mode, SCP bases node presence upon either the messagesnoted above or upon Data Link AP packet source node IDs. In this mode,nodes substitute the NCP_NetPresence message with an empty packet toassert presence, utilizing network bandwidth efficiently.

Since Data Link AP packet addresses are always sent in the clear, anode's presence can be spoofed. However, if this spoofing is done whilethe real node is active, SCP activates the Data Link imposter detectionmechanism. If the spoofing is done while the real node is inactive, noharm is done because the spoofing device cannot cause any action withoutsending valid (encrypted) Network layer AP messages.

An embodiment for security-critical applications implements anApplication layer presence protocol beyond the node presence detectionprovided by the Network layer. For example, an intruder or fire alarmmay require a minimum rate of operations, which causes a faultnotification if not maintained. Network load must be carefullyconsidered in such circumstances.

With respect to exemplary, presence protocol, whenever a node becomesactive on its logical network, the node sends a NCP_NetSignOn message totry to notify the other nodes of its presence. In one embodiment, thenode sends this message as a robust NCP message with normal priority.

If at all possible when reset or powered down, and whenever it isremoved from network membership, a node sends the NCP_NetSignOff messageto try to notify the other nodes of its absence. In one embodiment, thenode sends this message as a robust NCP message with high priority.

The Node identifier (ID) Node ID space is separated in two using thePresenceSlowBaseId application variable. Node IDs starting at this valueare tracked as slow presence nodes. The Network layer tracks presence ofevery other node on the logical network by sampling a presence table ata regular timed interval. If a node has sent a qualifying message duringthe last sampling interval, it is considered present on the network.This sampling interval is different for quick nodes and slow nodes, asset by the application variables PresenceFastTimeout andPresenceSlowTimeout.

In a further embodiment, it is the responsibility of each node to assertits presence on the network if it has not sent any qualifying messages(what qualifies depends on the presence mode the network is operatingin, based on the application variable RobustPresenceFlag) within thetime specified by PresenceFastRefresh or PresenceSlowRefresh (whetherits node ID is>=PresenceSlowBaseld). In robust mode, the node sends anNCP_NetPresence message, and otherwise an empty AP packet.

As alluded to earlier, refresh time variables are typically set at leasttwo times smaller than the matching time out variable for the network tooperate reliably.

Also, the values for these variables may be set statically by the devicemanufacturer or the installer based on its expected use. They may alsobe optimized dynamically by the ASA, using an application variablesdistribution mechanism and the PresenceLease value provided for eachdevice on the network.

The 'ZZZ application referenced above describes the use of applicationvariables in a distributed computing system. Application variables allowdynamic tuning and optimization of the protocol of logical network(s)under various operating conditions, which enables reliable operation inconnection with low bandwidth physical media. When very high bandwidthphysical media is utilized, some inefficiency can potentially beafforded because such inefficiency is hardly noticed from a performanceperspective. When a lower bandwidth physical media, such as PLC, isutilized, however, with potential noise considerations as well, dynamictuning of the network conditions is desirable. For instance, it may bethe case that certain message requests from a particular client/servernode combination reach the server node quickly and efficiently, however,the return responses to the client over the same physical mediaperiodically are lost, or arrive late. In such a case, it would bedesirable to dynamically determine that increased attention to thereturn responses is desirable. Since such inefficiencies with the returnresponses may occur intermittently and infrequently, it would bedesirable to be able to dynamically make such determinations. The 'ZZZapplication thus describes some exemplary non-limiting applicationparameters that may be utilized to tune the network optimally tooperating conditions. The present invention applies similar tuningtechniques, optimized for node presence tracking.

Application variables are thus network tuning parameters for a protocol,and may be utilized in connection with the node presence tracking of theinvention.

The following variables and corresponding non-limiting default valuesfor an exemplary SCP/PLC implementation of node presence tracking foruse in tuning network conditions are illustrated in Table I. TABLE INetwork Presence ID Name Time (sec, unless stated otherwise) 9 Slow NodePresence Base Id 1024 Node IDs 10 Fast Node Presence Refresh  10 11 FastNode Presence Timeout  25 12 Slow Node Presence Refresh  60 13 Slow NodePresence Timeout  150

In general, application variables can be thought of as relating to anyone or more of the following concepts pertaining to network conditions:data link, network, and transport. Presence variables are the relevantnetwork application variables optimized in accordance with theinvention.

While some exemplary embodiments herein are described in connection withsoftware residing on a computing device, one or more portions of theinvention may also be implemented via an operating system, applicationprogramming interface (API) or a “middle man” object, hardware,firmware, such that presence tracking may be included in, supported inor accessed via all of NET's languages and services, and in otherdistributed computing frameworks as well. There are thus multiple waysof implementing the present invention, e.g., an appropriate API, toolkit, driver code, operating system, standalone or downloadable softwareobject, etc. which enables applications, nodes, devices and services touse the presence tracking to achieve more complex functionality and moreefficient use of lower bandwidth media. The invention contemplates theuse of the invention from the standpoint of an API (or other softwareobject), as well as from a software or hardware object that communicatesin connection with presence tracking. Thus, various implementations ofthe invention described herein have aspects that are wholly in hardware,partly in hardware and partly in software, as well as in software.

As mentioned above, while exemplary embodiments of the present inventionhave been described in connection with various computing devices andnetwork architectures, the underlying concepts may be applied to anycomputing device or system in which it is desirable to implementapplication variables in a logical network. Thus, the techniques forproviding automatic network optimization with presence tracking inaccordance with the present invention may be applied to a variety ofapplications and devices. For instance, the algorithm(s) and hardwareimplementations of the invention may be applied to the operating systemof a computing device, provided as a separate object on the device, aspart of another object, as a downloadable object from a server, as a“middle man” between a device or object and the network, as adistributed object, as hardware, in memory, a combination of any of theforegoing, etc. While exemplary programming languages, names andexamples are chosen herein as representative of various choices, theselanguages, names and examples are not intended to be limiting. One ofordinary skill in the art will appreciate that there are numerous waysof providing object code that achieves the same, similar or equivalentfunctionality achieved by the various embodiments of the invention.

As mentioned, the various techniques described herein may be implementedin connection with hardware or software or, where appropriate, with acombination of both. Thus, the methods and apparatus of the presentinvention, or certain aspects or portions thereof, may take the form ofprogram code (i.e., instructions) embodied in tangible media, such asfloppy diskettes, CD-ROMs, hard drives, or any other machine-readablestorage medium, wherein, when the program code is loaded into andexecuted by a machine, such as a computer, the machine becomes anapparatus for practicing the invention. In the case of program codeexecution on programmable computers, the computing device will generallyinclude a processor, a storage medium readable by the processor(including volatile and non-volatile memory and/or storage elements), atleast one input device, and at least one output device. One or moreprograms that may utilize the application variables of the presentinvention, e.g., through the use of a data processing API or the like,are preferably implemented in a high level procedural or object orientedprogramming language to communicate with a computer system. However, theprogram(s) can be implemented in assembly or machine language, ifdesired. In any case, the language may be a compiled or interpretedlanguage, and combined with hardware implementations.

The methods and apparatus of the present invention may also be practicedvia communications embodied in the form of program code that istransmitted over some transmission medium, such as over electricalwiring or cabling, through fiber optics, or via any other form oftransmission, wherein, when the program code is received and loaded intoand executed by a machine, such as an EPROM, a gate array, aprogrammable logic device (PLD), a client computer, a video recorder orthe like, or a receiving machine having the signal processingcapabilities as described in exemplary embodiments above becomes anapparatus for practicing the invention. When implemented on ageneral-purpose processor, the program code combines with the processorto provide a unique apparatus that operates to invoke the functionalityof the present invention. Additionally, any storage techniques used inconnection with the present invention may invariably be a combination ofhardware and software.

While the present invention has been described in connection with thepreferred embodiments of the various figures, it is to be understoodthat other similar embodiments may be used or modifications andadditions may be made to the described embodiment for performing thesame function of the present invention without deviating therefrom. Forexample, while exemplary network environments of the invention aredescribed in the context of a networked environment, such as a peer topeer networked environment, one skilled in the art will recognize thatthe present invention is not limited thereto, and that the methods, asdescribed in the present application may apply to any computing deviceor environment, such as a gaming console, handheld computer, portablecomputer, etc., whether wired or wireless, and may be applied to anynumber of such computing devices connected via a communications network,and interacting across the network. Furthermore, it should be emphasizedthat a variety of computer platforms, including handheld deviceoperating systems and other application specific operating systems arecontemplated, especially as the number of wireless networked devicescontinues to proliferate. Still further, the present invention may beimplemented in or across a plurality of processing chips or devices, andstorage may similarly be effected across a plurality of devices.Therefore, the present invention should not be limited to any singleembodiment, but rather should be construed in breadth and scope inaccordance with the appended claims.

1. A method for providing presence tracking of nodes of a logicalnetwork having an underlying physical network medium in a distributedcomputing system, comprising: tracking by each node in the logicalnetwork the presence state of at least one other node; and optimizingbandwidth utilization of the physical network medium based upon thepresence state of at least one node in the logical network.
 2. A methodaccording to claim 1, wherein said tracking includes tracking by eachnode in the logical network the presence state of all other nodes in thelogical network.
 3. A method according to claim 1, wherein saidoptimizing includes ignoring communications to a node that has anassociated presence state that indicates the node is not in the presentstate.
 4. A method according to claim 3, wherein said optimizingincludes ignoring communications to a node that has an associatedpresence state that indicates the node is in the absent state.
 5. Amethod according to claim 1, wherein said tracking includes tracking thepresence state of at least one other node by periodically samplingwhether a keep alive message has been received.
 6. A method according toclaim 1, wherein said optimizing includes optimizing at least onevariable corresponding to a network layer of the protocol.
 7. A methodaccording to claim 6, further comprising: assigning values to the atleast one variable by an Address Space Arbitrator (ASA), wherein the ASAis an entity responsible for managing the network.
 8. A computerreadable medium for automatically tuning a network having an associatedprotocol and a plurality of nodes forming a logical network having anunderlying physical network medium having stored thereon at least onecomputer-executable module comprising computer executable instructionsfor performing a method, the method comprising: tracking by each node inthe logical network the presence state of at least one other node; andoptimizing bandwidth utilization of the physical network medium basedupon the presence state of at least one node in the logical network. 9.A computer readable medium according to claim 8, further includingasserting by each node on the network its presence state by sending aperiodic keep alive message.
 10. A computer readable medium according toclaim 8, wherein said tracking includes tracking the presence state ofat least one other node by periodically sampling whether a keep alivemessage has been received.
 11. A computer readable medium according toclaim 8, wherein the logical network has a node identification (node ID)address space for identifying each node and its associated values forsending and sampling keep alive messages.
 12. A computer readable mediumaccording to claim 11, wherein the node ID address space is split intotwo parts, wherein each part is assigned different values for sendingand sampling keep alive messages.
 13. A computer readable mediumaccording to claim 11, wherein said optimizing includes tuningparameters relating to how often a node sends and samples keep alivemessages.
 14. A computer readable medium according to claim 12, whereina first group of node IDs are assigned to fast presence devices, while asecond group of node IDs part are assigned to slow presence devices. 15.A distributed computing system capable of automatically tuning a logicalnetwork having an associated protocol and an underlying physical networkmedium, comprising: a plurality of nodes, wherein each node in thelogical network includes a presence tracking component that tracks thepresence state of at least one other node; and a tracking tableincluding the presence state of the at least one other node; whereinbandwidth utilization of the physical network medium is optimized basedupon the presence state of the plurality of nodes in the logicalnetwork.
 16. A distributed computing system according to claim 15,wherein the tracking table has a node identification (node ID) foridentifying each node and its associated values for sending and samplingkeep alive messages.
 17. A distributed computing system according toclaim 16, wherein the tracking table is split into two parts, whereineach part is assigned different values for sending and sampling keepalive messages.
 18. A distributed computing system according to claim16, wherein the network is optimized according to network tuningparameters relating to how often a node sends and samples keep alivemessages.
 19. A distributed computing system according to claim 16,wherein a first group of node IDs are assigned to fast presence devices,while a second group of node IDs part are assigned to slow presencedevices.
 20. A distributed computing system according to claim 16,wherein the tracking table is managed by an Address Space Arbitrator byusing a hint value provided in description information associated witheach node.